1. Field of the Invention
The present invention relates to an electronic unit, which includes a housing and a heat-generating electronic device stored in the housing. The heat generated in the device is transferred to the housing and efficiently transferred from the housing to the ambient air to cool the device.
2. Description of the Related Art
A proposed electronic unit includes a housing, which is made of metal such as aluminum, a plurality of heat-generating electronic devices, and a plate such as a ceramic substrate and a printed wiring board. The electronic devices are assembled on the plate. The plate assembled with the devices is stored in the housing. In the proposed electronic unit, each heat-generating electronic device is in contact directly with an inner surface of the housing, or a heat-conductive member is located between each device and the surface, so the heat generated in each device is conducted to the housing and transferred from the housing to the ambient air. To effectively transfer the heat from the housing to the ambient air, the housing of the proposed unit is relatively large or is air-cooled with a fan. If a fan is used, the proposed unit must be relatively large to accommodate the fan.
As a solution to the above issue, cationic electrocoating or anodic oxide coating is usually applied to the housing to improve heat radiation from the housing. Alternatively, a heat radiation material is proposed in JP-A-7-190675. The material improves the heat radiation properties of a body, to which the material is attached. The material is made of a mixture of dimetylsilicone, cordierite particles, and copper powders.
However, the cationic electrocoating, the anodic oxide coating, and the method of the publication require dedicated materials or apparatus, which are relatively expensive. Therefore, the production cost of the electronic unit is increased.
The present invention has been made in view of the above aspects with an object to provide an electronic unit, which is economy and compact and has desired heat radiation properties.
In the present invention, a sheet of paper, which has a thermal emissivity higher than a housing of the electronic unit, is adhered to an outer surface of the housing to improve the heat radiation from the housing to ambient air. Art paper, which is relatively affordable, is used for the sheet of paper.